As a liquid ejection apparatus for recording an image by ejecting liquid onto a recording medium, there is known an inkjet recording apparatus including a liquid ejection head in which a plurality of ejection ports for ejecting ink onto a recording medium is formed. In general, the number of tones (e.g., 2 to 4 tones) that can be expressed by the inkjet recording apparatus is smaller than the number of tones (e.g., 256 tones) in display image data (multi-value image data) displayed on a liquid crystal display provided in a host computer. Therefore, when an image according to multi-value image data is recorded on a recording medium, tones of the multi-value image data are quantized to be decreased to tones that can be expressed by the inkjet recording apparatus. As one of the methods for the quantization, an error diffusion process is known. The error diffusion process is image processing, in which a tone value is reduced and thereby an error generated in each pixel is diffused to peripheral pixels.
Further, with respect to the inkjet recording apparatus, in production of a liquid ejection head, an ejection amount of ink varies in each ejection port. Therefore, when an image is recorded on a recording medium using such a liquid ejection head, density nonuniformity is generated in the image recorded on the recording medium.